1. Field of the Invention
The present invention relates to an exposure apparatus and a device fabrication method.
2. Description of the Related Art
In recent years, a semiconductor device is increasingly packaged by flip-chip packaging. A process which fabricates a semiconductor device and copes with flip-chip packaging includes a process of forming a solder ball on a device. As a method of forming a solder ball, a plating method is known. In the method of forming a solder ball by plating, to bring a conductive film formed on a wafer (substrate) into contact with the electrode of a plating device (to electrically connect the conductive film to the electrode), it is necessary to peel off a portion, to be brought into contact with the electrode, in a resist formed on the conductive film. When the resist used is a negative resist, it is only necessary to prevent light from impinging on the peripheral portion of the wafer during exposure (that is, to shield the peripheral portion of the wafer against light). To do this, U.S. Pat. No. 6,680,774, for example, proposes a technique of placing a light shielding plate on the wafer during exposure.
Also, Japanese Patent Laid-Open No. 2005-286062 proposes an imprint apparatus which irradiates a resist on a wafer that is in contact with a mold with ultraviolet rays to transfer the pattern of the mold onto the resist. To define an irradiation region corresponding to each shot region on the peripheral portion of the wafer, Japanese Patent Laid-Open No. 2005-286062 discloses a technique of driving in the X- and Y-axis directions four light shielding plates having arcs corresponding to the contours of the wafer in the first to fourth quadrants, respectively.
As described in U.S. Pat. No. 6,680,774, when a light shielding plate is placed on the wafer, it must be retracted for every wafer replacement, thus imposing constraints in terms of space and throughput. Hence, a technique of placing a light shielding plate not on the wafer but on a plane optically conjugate to the wafer to have it shield the outer peripheral region of the wafer is available. In such a technique, a light shielding plate is positioned so that the distance from the outer periphery of the wafer to the boundary of the outer peripheral region stays constant (that is, the outer peripheral region shifted inward from the outer periphery of the wafer by a predetermined width is shielded against light), based on the position of each outer peripheral shot region on the wafer.
However, the wafer center position with reference to the outer shape of the wafer does not always coincide with the layout center position of an array (layout) of shot regions on a layer (underlying layer) formed on the wafer. When the wafer center position is shifted from the layout center position, but nonetheless the light shielding plate is positioned based on the position of each outer peripheral shot region on the wafer, the light shielding plate is positioned with an offset corresponding to the distance (shift amount) between the wafer center position and the layout center position. As a result, the distance from the outer periphery of the wafer to the boundary of the outer peripheral region varies in each individual outer peripheral shot region, so the width of the outer peripheral region shielded by the light shielding plate cannot be maintained constant.